Quantitative concentration profiling of nickel in tissues around metal implants: a new biomedical application of laser ablation sector field ICP-MS

Abstract

Laser-ablation sector-field (high resolution) inductively coupled plasma mass spectrometry (LA-HR-ICP-MS) has been used for in situ determination and spatial elemental profiling of nickel concentrations in tissues that have been exposed to nickel wire. Nickel has a number of adverse biological effects that have made the use of nickel (or any other metal) in biomedical implants controversial. Yet, information about the distribution of nickel in tissues around nickel-containing implants is scarce. This study examines the diffusion of nickel with time and the spatial distribution of nickel around nickel-containing implants in vivo. Pure nickel wires were implanted subcutaneously into rats for seven days and the tissues were analyzed for nickel content and degree of inflammation away from the implants using ²⁴Mg and ⁶⁰Ni isotopes. Data were obtained by ablation with Nd:YAG laser operating in the UV region (266 nm and 213 nm) and element analysis with a high resolution ICP-MS. A 50 ppm glass standard (NIST-612) was also analyzed for the same isotopes. Quantification was performed by assuming a uniform nominal magnesium concentration value of 97 µg g⁻¹ in untreated tissue and using ²⁴Mg intensity for internal calibration. The precision (RSD%) of measurements for ²⁴Mg for the NIST-612 Glass standard was within 3.8% to 4.6% and for the tissue samples was within 3.2% to 4.5%. The precision of analysis for ⁶⁰Ni for the NIST-612 Glass standard was 5.4%. There was a significant penetration of nickel ions into tissues exposed to nickel wire implants. The concentration of nickel reached values as high as 60 µg g⁻¹ near the implants, falling exponentially to undetectable levels 3–4 mm from the implants. The study showed that the laser ablation technique was well suited for analysis of soft tissues for metal ion content. This technique also allowed metal concentration spatial profiling as a function of time.